Construction and method of making prop shaft having enlarged end sections

ABSTRACT

An automotive prop shaft assembly particularly suited for coupling a transfer case to the front axle drive components comprises a tubular drive shaft having an initial uniform inner diameter relatively smaller than the outer diameter of a pair of forged insert yokes to be attached to the ends of the shaft. A section of each end of the tube is enlarged so that its inner diameter is sized to receive the yokes into the ends of the tube with an interference fit. The shaft and yokes are then welded together and weights fixed to the end sections to correct for imbalance.

This invention relates generally to propeller shaft assemblies forautomotive vehicles and particularly to the construction of the tubulardrive shaft portion and its connection with the end yokes of theassembly.

BACKGROUND OF THE INVENTION

Prop shaft assemblies of the above type are often used in automotiveapplications to couple the transmission and/or transfer case of avehicle to the axles in order to transfer power to the wheels.

In a typical prop shaft assembly, a pair of forged end yokes areprovided, each having an attachment collar at one end which is press fittogether with the opposite ends of a tubular drive shaft and then weldedto the shaft to secure them in place. In applications where there issufficient clearance to accommodate a large diameter drive shaft, it ispreferred that the drive shaft employed be one having an inner diametersufficiently large to accommodate the press fit insertion of the yokecollars into the ends of the shaft, as opposed to using a smallerdiameter drive shaft whose outer diameter enables the ends of the shaftto be extended into the collars. One reason the large diameter shaftconstruction is preferred is that it is comparatively simpler and morecost effective from a manufacturing standpoint to machine the outsidediameter of the yoke collars to prepare them for press fit extension andwelding within the drive shaft tube, rather than having to machine theinside diameter surface of the collar to accept the shaft.

In some applications, however, the available space for the prop shaftassembly, and particularly the clearance for the shaft which must extendlinearly between the yokes, is limited to such a degree that thepreferred large diameter drive shaft construction cannot be used. Atypical example of such limited clearance applications is front driveaxle arrangements, where the prop shaft competes for space with therouting of the exhaust system and various other components in thevicinity of the engine compartment.

The solution, thus far, to such limited space requirements has been toutilize the less desirable small diameter drive shaft construction. Inaddition to the machining difficulties mentioned above, a small diameterdrive shaft is more difficult and costly to balance. Balancing the shaftassembly involved applying weights to the end regions of the shaft tocompensate for any imbalance of the assembly. The smaller diameter driveshaft offers less area on which to mount the balancing weights, as wellas less net balance correction for attached weight due to the directrelationship between balance weight effectiveness and tube diameter andcertain accommodations must be made for the smaller shafts since much ofthe standard equipment used to support the assembly and apply theweights is set up for the large diameter assemblies.

SUMMARY OF THE INVENTION

According to the invention, a prop shaft assembly has an initial smalldiameter drive shaft whose outer diameter is sufficiently small toaccommodate a limited routing space environment. The opposite ends ofthe small diameter drive shaft are then enlarged in order that the innerdiameter of the end portions are sized to receive with a press fit thecollars of a pair of end yokes into the ends of the drive shaft tubewhich are then welded in the usual manner.

The invention thus provides a drive shaft that is a hybrid of sortsbetween the small and large diameter shafts mentioned above. The shafthas a small diameter mid-section that addresses the limited routingspace requirements of many front drive axle applications, yet has largediamater end sections to advantageously receive the collars of the yokesinto the ends of the shaft. Such hybrid construction thus combines thebenefits offered by both the large and small diameter drive shaft whileovercoming these limitations. The enlarged ends make it possible toutilize the preferred outer diameter machining of the yoke collars andfurther enable the shaft assembly to be balanced using standard balanceweights and balancing equipment designed for the large diameter tubeassemblies.

DRAWINGS

A presently preferred embodiment of the invention is disclosed in thefollowing description and in the accompanying drawings, wherein:

FIG. 1 is a longitudinal fragmentary front elevation view of a propellershaft assembly constructed in accordance with a presently preferredembodiment of the invention;

FIG. 2 is an enlarged fragmentary exploded view of the prop shaftcomponents of FIG. 1 with the shaft in a pre-enlarged, pre-assembledcondition; and

FIG. 3 is an enlarged fragmentary longitudinal view, shown partly insection, of an end of the prop shaft assembly.

DETAILED DESCRIPTION

Referring now to FIG. 1, an automotive propeller shaft assemblyconstructed in accordance with a presently preferred embodiment of theinvention is indicated generally by the reference numeral 10 andcomprises an elongate drive shaft 12 having yokes 14, 16 attached to itsopposite ends.

The yokes 14, 16 are forged components, each having a connecting collaror shank 18 at one end presenting an outer mating surface 20 machined toa predetermined diameter D_(y). Laterally spaced ears 22 are formed atthe opposite end of the yokes 14, 16. The ears 22 are formed withaligned cross holes 24 for journaling, in the usual manner, a spider 26carried by another yoke 28 to provide a Cardan-type universal joint ateach end of the shaft 12.

The shaft 12 comprises a longitudinally extending length of cylindricalmetal tubing material having opposite open ends 30, 32 thereof.Initially, the tubular shaft 12 is of uniform small diameter along itslength so as to be undersized with respect to the yokes 14, 16 that isattached to. The shaft 12 has an initial outer diameter D_(o) that isrelatively smaller than that of the diameter D_(y) of the yoke shanks18. The small outer diameter size of the tube 12 is selected tofacilitate linear routing of the shaft 12 in applications where space islimited, such as, for example, in automotive front axle applications forcoupling a vehicle's transfer case to the front axle drive components.

In the example illustrated, the shaft has an initial outer diameterD_(o) of about 44.5 mm with a uniform minimum wall thickness of about2.4 mm and an overall length dimension of about 679-740 mm. Whilespecific dimensions and ranges are given above for purposes ofillustration, those skilled in the art will appreciate that otherdimensions are possible and contemplated by the invention based on theparticular space limitations and length requirements for the particularapplication.

The tubular shaft 12 has an initial inner diameter D_(I) that isgoverned in part by the initial outer diameter D_(o) and the wallthickness of the tube but, in any event is smaller in diameter than thatof the outer diameter D_(y) of the yoke collars 18.

In accordance with the invention, opposite end sections 34, 36 of theshaft 12 are enlarged to an expanded inner diameter D_(e) of sufficientsize to provide a press fit connection with the collar 18 of the yokes14, 16. In example illustrated, the shaft 12 has an expanded innerdiameter D_(e) in the range of about 49.2 to 49.33 mm, which correspondsin size with the diameter D_(y) of the yoke collars 18. The smalldiameter midsection 38 of the shaft is unaffected by the enlargement ofthe end sections 34, 36 and as such retains the original diameter andwall thickness dimensions.

The enlargement of the end sections 34, 36 of the shaft 12 may be carredout by a mechanical forming or flaring operation in which the shaft 12is clamped in a fixture (not shown) and an enlarged forming mandrel (notshown) extended into each of the open ends 30, 32 to stretch the tubing12 in the vicinity of the end sections 34, 36 to the enlarged innerdiameter D_(e). The enlargement of the end sections 34, 36 produces acorresponding reduction in their wall thickness by about 0.3 mm.

As illustrated best in FIG. 3, the length of the enlarged end sections34, 36 is relatively greater than that of the length of the yoke shanks18. The extended length provides a region 42 inward of the yokes 14, 16for engaging and supporting the shaft 12 during insertion of the collars18 into the ends of the shaft 12. The region 42 further provides alocation for engaging and supporting the shaft 12 by a standard largediameter balancing fixture (not shown) and for attaching one or morestandard large diameter balance weights 44 along each of the endsections 34, 36.

After the enlarged end sections 34, 36 have been formed, the yokes 14,16 are attached by press fitting the shanks 18 of the yokes into theopen ends 30, 32 of the end sections 34, 36 until the end of the shaft12 confront abutting shoulders 14a, 16a of the yokes 14, 16,respectively. The yokes 14, 16 are then fixed permanently to the shaft12 by weldments 46 in the usual manner.

The balance weights 44 are selected and secured preferably by welding inthe appropriate locations on the end sections 34, 36 to correct anyimbalance of the assembly 10. The extended length of the end sections34, 36 enables the weights 44 to be attached at a locationlongitudinally spaced from the insert shanks 18 of the yokes 14, 16 soas not to impair the integrity of the yoke-to-shaft weldments 46.

The disclosed embodiment is representative of a presently preferred formof the invention, and is intended to be illustrative rather thandefinitive thereof. The invention is defined in the claims.

We claim:
 1. A method of manufacturing an automotive prop shaft assemblycomprising the steps of:providing a pair of end yokes each having aninsert collar of a predetermined outer diameter; providing an elongatemetallic tubular drive shaft member having opposite ends and an initialuniform inner diameter relatively smaller than that of the outerdiameter of the collars; expanding the inner diameter of each end of theshaft to form enlarged end regions each having an enlarged innerdiameter sized to provide an interference fit with the collars of theyokes; press fitting the collars of the yokes into the enlarged endregions of the shaft; and welding the yokes to the shaft to formpermanent metallic bonds therebetween.
 2. The method of claim 1including providing a shaft having an initial outer diameter that isrelatively smaller than the outer diameter of the collars.
 3. The methodof claim 1 including attaching balance weights to the enlarged endsections of the shaft.
 4. The method of claim 3 wherein the balanceweights are attached to the shaft in longitudinally spaced relation tothe collars.
 5. The method of claim 1 wherein the collars have apredetermined length and the end sections are formed with a length thatis relatively greater than that of said collars.
 6. The method of claim5 wherein the lengths of the end sections are formed sufficiently longto accommodate the attachment of balance weights to the end sections ata location longitudinally spaced from the collar of the yokes.
 7. Amethod of manufacturing an automotive prop shaft assembly comprising thesteps of:providing a pair of end yokes each having collars ofpredetermined outer diameter; providing a tubular drive shaft having aninitial inner diameter relatively less than that of the outer diameterof the collars; expanding the shaft at its opposite ends to formenlarged end regions each having an enlarged inner diameter sized toprovide an interference fit with the collars of the yokes and being ofsuch length to accommodate the mounting of the balancing weights on theenlarged edge regions; press fitting the collars of the yokes into theenlarged end regions of the shaft; and welding the yokes to the shaft.